Inclusion Complexes of N -Benzoyl-d-Leucine and N -Benzoyl-l-Leucine with β-Cyclodextrin by Raman Spectroscopy

We report what is believed to be the first detection of chiral recognition in the inclusion complexes of cyclodextrins by Raman spectroscopy. The spectra of inclusion complexes of N-benzoyl-d-leucine or N-benzoyl-l-leucine with β-cyclodextrin were recorded in the 1500–1800 and 3000–3150 cm⁻¹ regions. These chiral molecules were chosen to provide group frequencies (NH₂⁺ and benzoyl C=O) near the chiral center of the guest as well as COO⁻ and phenyl CH for probing the guest molecule without spectral interference from the vibrational bands of the cyclodextrin host. Frequency shifts and intensity decreases were observed for some Raman bands of N-benzoyl-leucines upon inclusion in the cyclodextrin cavity. In the Raman spectra of the inclusion complex, the frequency shifts were greater for N-benzoyl-d-leucine than for N-benzoyl-l-leucine.